Anyone know if a 200Ah lithium battery is overkill for a small shepherd's hut?

Got a shepherd's hut project on the go and trying to figure out battery sizing before I pull the trigger on anything.

The hut is pretty modest — think weekend retreats, maybe the odd week here and there. Loads are basically:

• LED lighting (maybe 3-4 lights)
• A 12v compressor fridge
• Phone/laptop charging
• Occasionally a small fan in summer

Running a pair of 100W panels on the roof, which feels about right for the footprint.

My question is whether a 200Ah lithium (looking at Fogstar Drift or similar) is genuinely useful here or whether I'd be better off with a 100Ah and saving myself a couple of hundred quid.

The fridge is probably the main draw — I've seen figures anywhere from 30-60Ah per day depending on ambient temp, which is a massive range tbh. UK weather being what it is, I'm not always going to get a full charge either.

Is the extra capacity worth it for those cloudy stretches, or am I overthinking it? Anyone running a similar setup who can share actual real-world consumption figures rather than theoretical ones?

@OllieThompson73 — done exactly this kind of sizing exercise for my narrowboat and static caravan setups, so I've got a feel for it.

200Ah is not overkill if you're factoring in a few cloudy days with no solar input. Lithium's real usable capacity is around 80-90%, so you're working with roughly 160-180Ah in practice.

The question is really what are you running? Lighting and phone charging versus a compressor fridge and a hot water pump are very different conversations.

For a weekend hut with modest loads, a Fogstar 100Ah might actually be the smarter starting point — cheaper, lighter, and you can always add a second unit later. That modular approach saved me a fortune when I was figuring out my actual consumption versus what I thought it would be.

What's your solar panel situation looking like?

200Ah is probably fine but without knowing your actual loads it's just a number pulled from thin air — run the maths: watts × hours = Wh, divide by your battery voltage, add 20% for inverter losses, then decide if you actually need it or if a decent 100Ah Fogstar Drift would do the job for half the money.

Shepherd's huts typically murder batteries with one thing nobody accounts for: a small electric heater someone plugged in "just for ten minutes" — budget for that or you'll be staring at a flat pack by Sunday morning.

If you're going Victron for the BMS/MPPT side (which you should), the app will at least tell you exactly how badly you've misjudged your consumption after the first weekend.

@OllieThompson73 — I'll tell you what nobody mentions until it's too late: usable capacity is the real figure that matters, not the headline number.

I've done three off-grid builds now — narrowboat, van, and a mate's tiny house — and every single one started with "is this overkill?" then ended with "wish we'd gone bigger."

With lithium (Fogstar or similar) you're getting roughly 80-90% usable. A 200Ah bank gives you maybe 170Ah in practice. Run a decent 12V fridge and you've chewed through half that overnight before you've even thought about lighting.

Weekend use with solar topping it up daily? 200Ah is probably the minimum I'd consider, not overkill. Especially if you ever want to extend stays or add loads later.

Size it once, size it right.

@OllieThompson73 honestly for a weekend retreat I'd say 200Ah is probably just right rather than overkill — I've got a similar-ish setup in my garden office and some days I'm really glad I didn't go smaller when there's a run of cloudy days.

What I'd add to what @Rob1963 and @WezFisher have said — don't just size for today's loads, size for creep. You'll add a lamp, a small fan, a phone charger dock... it happens every time 😄

Also worth looking at Fogstar Drift for the actual cells — cracking value for UK buyers. Pair it with a decent Victron MPPT and you're sorted.

The real question is how many panels are you planning? Battery size and solar input need to work as a pair really.

@OllieThompson73 worth thinking about whether you'll ever want to expand — I started with 100Ah in my tiny house thinking it'd be plenty, ended up bolting on a second unit within six months. Pain to retrofit properly.

If budget allows, 200Ah LiFePO4 gives you headroom without going daft. Fogstar do decent cells at reasonable prices if you're watching the pennies.

One thing nobody's flagged yet — charge source matters as much as capacity. A 200Ah bank with undersized solar panels will sit half-empty half the time anyway, especially through a UK autumn/winter. What's your panel setup looking like?